Digital printing apparatus

Abstract

A digital printing apparatus including a sheet supply device, printing cylinder, inkjet nozzle portion, sheet delivery device, and conveyance devices. The sheet supply device supplies sheets one by one at a predetermined period. The printing cylinder includes at least one gripper device that grips and holds the sheet, and conveys the sheet while one edge of the sheet supplied from the sheet supply device is held by the plurality of gripper devices. The inkjet nozzle portion discharges ink droplets onto the sheet. The conveyance devices include a plurality of gripper devices including one reversing gripper device that grips and holds the other edge of the sheet, and conveys the sheet printed on one surface, which is received from the printing cylinder in a double-sided printing mode. The sheet is turned by reversing the obverse/reverse surface of the sheet by the reversing gripper device in the process of conveyance.

What is claimed is: 
     
       1. A digital printing apparatus comprising:
 a sheet supply device which supplies sheets one by one at a predetermined period; 
 a printing cylinder which includes at least one gripper device that grips and holds the sheet, and conveys the sheet while one edge of the sheet supplied from said sheet supply device is held by said at least one gripper device; 
 an inkjet nozzle portion which discharges an ink droplet onto the sheet conveyed by said printing cylinder, and prints on the sheet; 
 a sheet delivery device which discharges the sheet after end of printing by said inkjet nozzle portion; 
 conveyance devices which include a plurality of gripper devices including one reversing gripper device that grips and holds the other edge of the sheet, convey the sheet printed on one surface, which is received from said printing cylinder in a double-sided printing mode, while sequentially transferring the sheet by gripping changes by said plurality of gripper devices, and supply to said printing cylinder the sheet turned by reversing an obverse/reverse surface of the sheet by said reversing gripper device in the process of conveyance; 
 an upstream sheet conveyance device which transfers the sheet from said sheet supply device to said at least one gripper device of said printing cylinder; 
 a sheet presence/absence detection device which is provided on a downstream side, in a sheet conveyance direction, of a sheet reception position at which the sheet is received from said upstream sheet conveyance device of said printing cylinder, and on an upstream side, in the sheet conveyance direction, of a printing position at which printing is performed by said inkjet nozzle portion, and detects presence/absence of a sheet on said printing cylinder; 
 a drying device which is provided on an upstream side of the printing position of said printing cylinder in the sheet conveyance direction, and dries ink printed on the sheet; 
 a phase detection device which detects a rotary phase of said printing cylinder; and 
 a control device which controls said drying device based on the outputs from said sheet presence/absence detection device and said phase detection device, so as to stop a drying operation when a support surface which supports no sheet on said printing cylinder is opposed to said drying device. 
 
     
     
       2. A digital printing apparatus comprising:
 a sheet supply device which supplies sheets one by one at a predetermined period; 
 a printing cylinder which includes at least one gripper device that grips and holds the sheet, and conveys the sheet while one edge of the sheet supplied from said sheet supply device is held by said at least one gripper device; 
 an inkjet nozzle portion which discharges an ink droplet onto the sheet conveyed by said printing cylinder, and prints on the sheet; 
 a sheet delivery device which discharges the sheet after end of printing by said inkjet nozzle portion; 
 conveyance devices which include a plurality of gripper devices including one reversing gripper device that grips and holds the other edge of the sheet, convey the sheet printed on one surface, which is received from said printing cylinder in a double-sided printing mode, while sequentially transferring the sheet by gripping changes by said plurality of gripper devices, and supply to said printing cylinder the sheet turned by reversing an obverse/reverse surface of the sheet by said reversing gripper device in the process of conveyance; 
 an upstream sheet conveyance device which transfers the sheet from said sheet supply device to said at least one gripper device of said printing cylinder; 
 a sheet conveyance failure detection device which is provided on a downstream side, in a sheet conveyance direction, of a sheet reception position at which the sheet is received from said upstream sheet conveyance device of said printing cylinder, and on an upstream side, in the sheet conveyance direction, of a printing position at which printing is performed by said inkjet nozzle portion, and detects a conveyance failure of the sheet; 
 a nozzle head moving device which brings said inkjet nozzle portion close to said printing cylinder or separates said inkjet nozzle portion from said printing cylinder, said nozzle head moving device including an inkjet nozzle attaching/detaching device which moves said inkjet nozzle portion between a printing position at which said inkjet nozzle portion comes close to said printing cylinder to print on the sheet, and a retreat position at which said inkjet nozzle portion retreats radially outside said printing cylinder; and 
 a control device which controls said nozzle attaching/detaching device based on the detection output of said sheet conveyance failure detection device during printing to move said inkjet nozzle portion from the printing position to the retreat position. 
 
     
     
       3. An apparatus according to  claim 2 , further comprising:
 sheet thickness input/detection means which detects or receives a thickness of the sheet, 
 wherein said nozzle head moving device further comprises a head position adjusting device which adjusts a position of said inkjet nozzle portion with respect to said printing cylinder at the printing position, and 
 said control device controls said head position adjusting device based on the sheet thickness output from said sheet thickness detection/input means to adjust a gap between said inkjet nozzle portion and the sheet conveyed by said printing cylinder.